Communication devices and transmission devices (hereinafter, collectively referred to as “communication devices”) such as network switches and servers are connected to other communication devices via communication cables in some cases. For example, a communication module provided at one end of a communication cable is connected to one communication device, and a communication module provided at the other end of the communication cable is connected to the other communication device. Specifically, one communication module is inserted in a slot provided in a front panel, a rear panel or the like of one communication device, and the other communication module is inserted in a slot provided in a front panel, a rear panel or the like of the other communication device. The communication module inserted in each of the slots is connected to a connector provided behind the slot. In the following description, the front panels, rear panels and the like of the communication devices provided with the slots to and from which the communication modules are inserted and removed will be collectively referred to as “panels” in some cases.
Herein, in order to realize further performance improvement and reduction in power consumption, it has been strongly desired for communication devices to realize high-density mounting. Under such circumstances, more communication modules than before are desired to be attachable to a communication device. In other words, more slots than before are desired to be provided on the panel of the communication device.